Sound-reproducing instrument



Oct. 30, 1928. 7 1,689,788

7 L. G. LARSEN SOUND RE PRODUCI NG I S TRUMEN'I Filed Aprill, 1925 s Sheets-Sheet 1 INVENTOR 1011/5 6? AWSEN ATTORNEY Oct. 30, 1928.

L. G. LARSEN 5 Sheets-Sheet 2 INVENTOR Z. 00/5 61 L HRSEN @ZMMM ATTORNEYS 1,689,788 L. c. LARSEN SOUND REPRODUCING INSTRUMENT Filed April 1, 1925 5 Sheets-Sheet 3 I, P Wi/AI i g lll WHMIH lllllllllllmml lfllllllillllllll INVENTOR O Aloous (2Z/w?svV M ATTORNEY Patented Oct. 30, 1928.

PATENT OFFICE.

LOUIS G. .LARSEN, OF JERSEY.CITY, NEW JERSEY.

SOUND-REPBODUCING INSTRUMENT.

Application filed April 1, 1925. Serial No. 19,813.

This invention relates to sound reproducing instruments and .has for its principal object to provide a new and improved construction and arrangement in a sound reproducer, of a plurality of diaphragms for improving the tonal qualities of instruments of this character.

A further object is to provide electrical means for vibrating the plurality of diahragms and to combine therewith means ror permitting any one or all of the diaphragms to be operated selectively.

Another object of the invention is to improve upon the construction and arrangement of that type of sound reproducers known as loud speakers such as are used for transforming audio-frequency waves into sound waves.

A. further object is to provide anew and improved construction, mounting, and arrangement oi. the members of the so called loud speaker unit whereby the efficiency of the unit is increased and the constructional details are simplified.

These and other obJects such as the provision of a compact instrument of neat and attractive appearance, the reduction of man'- ufacturing costs, and durabilityof construction will appear more fully from the following more detailed specification and by reference to the accompanyin forming a part hereof and wherein two illustrative examples of constructions embodying the principles of my invention are shown.

In the drawings, Fig. 1 is a central vertical section through a loud speaker embody- .ing my invention; Fi 2 is a section on the line 2-2 of Fig. 1; ig. 3 is an end elevation partly in section of the structure shown in Fig. 1 and as seen from the left hand side of said figure; Fig. 4 is a section on the line 4-4 of Fig. 2; Fig. 5 is a viewsimilar to Fig. 1- of a modified construction and Figs' 6, 7 and 8 are sections on the lines 6-6, 7-7 and 8-8 respectivel of: Fig. 5.

In the form shown in Figs. 1, to 4 inclusive, the loud speaker or tele hone unit consists of a suitable base 10, aving secured thereto, asby the screws 11 a bracket 12 which serves as a support for an electromagnet consisting of a coil 13 and a core piece 14'. A permanent magnet 15 formed of a relatively thick U-shaped piece of metal is also mounted upon the base 12 and is clamped at its center upon a post 16, by'any drawings suitable means such as the bolt 17 and nut 18 the poles of the magnet terminating a short distance from, but to one side of, the poles of the core piece 14 of the electromagnet. A pair of vibrators 19, 20, is secured to the ermanent magnet 15 one adjacent each p0 e thereof, said vibrators having their inner ends clamped rigidly to the magnet 15 by any suitable means such as the bolts 21, while their outer'ends extend outwardly beyond the poles of said magnet .15 and terphragm 23 for a purpose which will be presently described. Said diaphragms have their'outeredges clamped between the vertic'al, annular flanges 24 and 25 provided respectively on the base 10 and the ends of the branchconduits 26, 27 which lead to the horn 28; said flanges being clamped together adjacent to their peripheries by a plurality of screws 29.

The centres of the diaphragms 22 and 23 are connected respectively to the vibrators 19, 20 by means of the pins 20, the ends of which are rigidly secured to their respective.

vibrators and diaphragms.

The branched conduits merge at their upper ends vinto a cylindrical neck 31 having a central dividin web or partition 32.

.The neck of the horn 28 is reduced and threaded to engage within the threaded intorior-ot the neck 31, and said horn is also provided with a partition 33 adapted to align with the partition 32 when the horn is screwed into place. The partition 33 extends along the longitudinal centre of the horn and terminates within the bell (not shown) of the horn close to the mouth thereof. The branched conduits-26, 27 and the telephone unit form a unitary structure which is held in position within the housing 34 by the clamping engagement of the necks of the horn and branched conduit with the apertured top 35. of the housing 34.

As it may be .found desirable at times to use either one of (the diaphragms only, I

provide means for selectively interrupting the operat on of the vibrators and such means may comprise the rods 36, one or each diaphragm and mounted in suita le bearings 37 for longitudinal sliding motion. The outer end of each rod projects through the housing 34 and is provided with an oper-.

ating head or button 39, while the inner end of each rod terminates in a conical or wedge shaped point 38, to provide an inclined face adapted when the rod is pushed inwardly to engage the outer end of its respective vibrator and force it into contact with its co -operating pole of the core piece 14 of the electromagnet. When either one of the v1- brators are thus forced into contact with the core of the magnet, it will be seen that its co-operating diaphragm will not be vibrated, at the same time the volume of the instrument will not be materially decreased because the placing of one of the vibrators in contact with the core'of the magnet eliminates one of the air gaps with the result that the strength of the magnetic field which influences the other vibrator is increased thereby increasing the amplitude of the vibrations of the diaphragm connected with the latter. It will be understood that both of the vibrators 19 or 20 may be left free to operate or either may be made inoperative "as desired. The rods 36 maybe provided with suitable stops to limit their movement to operative and inoperative positions.

In the form shown in Figs. 5 to 8 inclusive, I provide. a pair of coils 40, 41,,secured to the ends of a U-shaped magnet 42, said coils being provided with the hollow sleevelike core pieces 43, which pass through the axial centers of the coils and through the arms of the U-shaped magnet, the ,cores being fixed against movement relatively to and serving to secure the coils andmagnets together to form a unitary assemblage of these parts. This assemblage is mounted within a keyhole-shaped slot 45, formed in asupporting block 46, by slidingthe parts longitudinally into position, set screws 47 preferably being provided to hold said parts in set position. The inner ends of the core pieces and coil are spaced from each other as clearly shown in Figs. 5and 6 and a pair of vibrators, formed of a single piece of material 48, has their free ends pro'ecting into the space or gap between sai coils, and terminating in alignment with but slightlyv spaced from the ends of the core.

pieces 43. The vibrators 48 are secured by their central connecting portion to a disk 49 adjustably fixed, as by screws 50, to the su porting block 46.

eans are provided for adjusting the gap between the ends of the core pieces and the free ends of the vibrators, and such means comprise a air of pins 51, slidably mounted within the oles 52 drilled into the supporting block. Adjusting screws 53 having cone-shaped inner ends project into the holes 52, with their cone shaped ends in contact with the inner ends of the pins 51 and serve to force the outer ends of said pins into contacting engagement with the connecting central portion of the vibrators 48.

Secured to opposite sides of the supporting blocks 46, by any suitable means, such as the screws 54, is .a pair of circular plates 55, 56 of different diameters. Each of said plates has an outwardly projecting annular flange or rib adjacent to its periphery against which theiouter portions of the diaphragms 57, 58 are clamped by the clamping rings 59, 60. The centers of the diaphragms 57, 58 are connected to the cooperating free ends of the vibrators 48 by means of the pins 61 which pass freelv through the centers of the hollow core pie"es 43. I

The supporting block 46 is provided with an upwardly extending hollow boss 62 having a central partition 63 to divide said boss into a pair of conduits 64, 65 which com-.

' duced threadedend of the neck of the horn 28 which, when screwed into position clamps the telephone or loud speaker unit, carried by the block 46, and holds it suspended with- .in the housing 68.; the construction of the,

horn and the manner of clamping the unit in place within the 'housingbeing the same as shown in Figs. 1 to 4.

The operation of the instrument shown in Figs. 1 to 4"is as follows: As heretofore pointed out the permanent magnet 15 is secured ,only at its central portion, thus leaving the ends or poles thereof freefor vibration and the poles ofsaid magnet are arranged opposite to the opposite poles of the core pieces 14.

When the audio-frequency current is passed through the coil 13 the oscillations thereof will produce variations in the mag netic field in accordance with the well known principles. These variations will attract and repel the vibrators 19, 20 which because of their connection with the diaphragms '22, 23, by the pins 30 will produce corresponding'vib'rations in the diaphragms, thus setting up vibrations or sound waves in the pair of air columns in the branched conduits 26, 27 v and born; the soundsthus reproduced issuing from the horn in the usual manner.

By em loying two different sized diaphragms aving' different normal periods of vibrations or fundamentals andby maintaining the air columns vibrated by said diaphragms separated or isolated the one from the other until the sounds merge at the mouth of the horn I obtain a marked improvement in the quality or tone of the sound reproduction over the usual instruments employing a single diaphragm only. This improvement in tone being due to the fact that the larger diaphragm reproduces lower tones with more fullness, while the smaller diaphragm reproduces the higher tones with greater clarity and sharpness. At the same time as the vibrations of the different diaphragms are produced by the same electrical oscillations, the differences in the tones produced by the vibrations of two diaphragms are merely such that a neutralizing effect seems to .be exerted by one setof sound poles of the core piece 14, as in this way the amplitude of the oscillations of the diaphragms are increased because the magnetic field acting upon the vibrators, which form in effect a continuation of the'magnet 15 and form the poles thereof, is the combined field due to the permanent magnet 15 and also to the induced and residual magnetism of the core 14.

The operation of the modification shown in Figs. 5 to 8 is the same in principle as that of the form shown in Figs. 1 to 4, the coils 40 and 41 connected in series being similar in function to the coil 13., In this form, however, I may employ spring steel for the vibrator 48 and construct the pins If the pins are of soft iron,

(ll of soft iron. they act as armatures and contribute to the vibratory effects producedupon .the free ends of the vibrator by the magnetic attraction of the core pieces 43 of the elecetromagnet.

lVhile I have shown the neck portion only of the born 28, it will be understood that such horn is provided with a bell month which may be of any desired shape or size. It will also be understood that the rods 36 may be employed equally as well with'the construction shown in Figs. 5 to 8 inclusive,

as with the construction shown in Figs. 1 to 4. Likewise it will be understood that many changes, variations and modifications of the relative arrangement and sizes of the parts may be resorted to without departing from the spirit of my invention.

I claim:

1. In a sound reproducer, an electromagnet, vibrators mounted adjacent to the poles of said magnet, a pair of diaphragms connected with said vibrators and means for selectively preventing the vibration of either of said diaphragms.

2. In a sound reproducer, an electromagnet, vibrators mounted adjacent to the poles of said magnet, a pair of diaphragms connected with said vibrators, and means for selectively preventing vibration of either of said vibrators, said means comprising a pair of members movable into and out of contact with said vibrators. 3. In a sound reproducer, an electromagnet having a central core iece, a permanent magnet having a pair of vibrators secured to its poles and terminating adjacent to the poles of said electro-magnet, but spaced therefrom to provide a pair of air gaps, and means for selectively preventing the operation of either of said vibrators and for simultaneously pressing such vibrator against the adjacent pole of said electro-magnet to close one of said air gaps, and thereby increase the intensity of the magnetic field in the reigon of said other vibrator.

4. In a sound reproducer, a pair of diaphragms, an electro-magnet for vibrating both of said diaphrgams in unison and means for preventing the vibration of one of said diaphragms while permitting the vibration of the other.

5. In a sound reproducer, a pair ofdiaphragms, a single electro-magnet having a pair of vibrators and connections therefrom to said diaphragms, and means for causing substantially the entire magnetic influence of said magnet to be exerted for vibrating one of said vibrators while simultaneously preventing vibration of the other vibrator.

In testimony whereof I have hereunto set my hand.

LOUIS G. LARSEN. 

